1. Technical Field of the Invention
The present invention relates to a fader position detection apparatus and a fader position control apparatus. More specifically, the present invention relates to a technology capable of accurately acquiring position data and moving a sliding piece of the fader to a target position despite a variance of accuracy of the electric fader's variable resistor and despite a variance of mounting positions of the faders on an operation panel.
2. Prior Art
Conventionally, an audio system such as a digital mixer often uses an operation panel containing an electric fader to set various parameter values (e.g., see patent document 1). The electric fader has a variable resistor that moves in interlock with a sliding piece. When the sliding piece is manually operated, its operated position is detected as a voltage value or a current value that varies with a resistance value of the variable resistor. An A/D converter converts the voltage value or current value into a digital value. The converted value is supplied as position data to a system CPU that controls the digital mixer. The CPU converts the supplied position data into an attenuation factor and saves it in a current memory. The CPU then supplies the attenuation factor to a DSP (digital signal processor) in a signal processing section of the digital mixer. During the mixing process of audio signals, the DSP controls attenuation factors of each channel corresponding to each fader in accordance with the supplied attenuation factor value.
The electric fader has a motor drive section for setting the sliding piece to a specified position. For example, the digital mixer stores setting data as a scene for mixing audio signals including each attenuation factor of each channel. Some digital mixers have a function of recalling (invoking) the scene to resume the specified state of mixing. When the scene is recalled, the CPU reads the setting data (including the attenuation factors) for the scene, and copies it to the current memory. The sliding piece of the corresponding fader is electrically moved to a specified position so that the sliding piece position matches a position corresponding to the attenuation factor value. The same applies to the auto-mix function that automates all mixing operations. When a fader moving event is reproduced at a specified timing according to the time stamp during auto-mix reproduction, the fader's sliding piece is electrically moved to a position corresponding to the attenuation factor specified by that event.
The electric fader is provided with a mechanism to turn off the electrical driving when a user manually commences operation of the fader's sliding piece while it is driven electrically.
The above mentioned Patent document 1 is Japanese Patent Publication No. 2684808
The conventional electric fader is subject to a variance of variable resistor accuracies and, therefore, subject to a variance of operation positions to be detected. Since resistance changes are uneven depending on positions of the fader's variable resistor, for example, this may degrade the linearity of detected fader positions. The fader is provided with a scale of graduations such as 0 dB and −10 dB to indicate the current position of the sliding piece. Positioning the sliding piece to a particular graduation does not necessarily provide an accurate attenuation factor indicated by the graduation, since there is always a mechanical error.
Further, it is possible to provide a plurality of faders with the same attenuation factor and electrically drive the sliding pieces so as to be moved to the position corresponding to the same attenuation factor. In this manner, the sliding pieces of the faders should all align to the same position horizontally. However, there have been cases where the sliding pieces of the faders are misaligned due to variable resistor errors of the faders. On the other hand, even if sliding pieces of the adjacent faders are manually adjusted to the same position, the faders do not necessarily generate the same attenuation factor due to possible errors.
When the operation panel of the digital mixer system is repaired to replace a faulty fader, a replaced new fader must conform to the characteristics of the other faders. Otherwise, the above-mentioned problems occur. Further, the replacement fader must be precisely aligned to the mounting position.